THE GRATEFUL DEAD'S Bob Weir and San Anselmo auto mechanic Tommy Olivier have been friends for more than 20 years. Buddies might be a better word for their relationship, which was forged on the gridiron as teammates on the Tamalpais Chiefs, perennial powerhouse of the Mill Valley Flag Football League. After games, the Chiefs would adjourn to the 2 A.M. Club, where suds were poured and the TV was always tuned to an NFL game.

"We'd watch the pros play and knock a few beers back and everyone would tell each other how they beat up on each other," Weir recalled.

Off the field, though, the rock star and the regular guy would seem to have little in common. But Weir and Olivier, affectionately known as Tommy O, have always enjoyed each other's company, going on hikes together, working out together, cracking each other up.

One of Olivier's friends once asked him why he got along so well with Weir, co-founder of a legendary band, a member of the Rock and Roll Hall of Fame. Wasn't he even a little star-struck by his friend's celebrity? Uh, no. Quite the opposite.

"I accept him for the kook he is," Olivier said with a snicker.

"I can be a total dickhead and he just laughs me off," Weir added.

Over the years, when one or the other was going through a tough time, they always had each other's backs. Since March, that loyalty has meant more than it ever has before. That's when the 50-year-old Olivier was diagnosed with

metastasized cancer, when doctors discovered 15 melanoma tumors in his brain and several more in his torso.

"That was kind of out of the blue, but I didn't go, 'Why me?,'" Olivier remembered. "I didn't dwell on it. I just said, 'OK, this is what it is, what are we going to do about it?'"

Since then, he's undergone brain surgery to remove a tumor that was pressing on his spinal fluid. That was followed by 10 days of radiation treatments. Another round of treatments has recently been halted, and he's waiting to hear the results.

When he does, he's sure to keep his friends posted through the website Caring Bridge. He's had something like 9,000 visitors to his site so far, which tells you how many friends he has. But none better than Weir, especially now.

"If anything, our friendship has strengthened," Olivier said. "He's watching out for me a little more, checking in on me, even though I tell him I don't need it."

Even with health insurance, Olivier still faces mounting medical costs. To help with those and other expenses, Weir has organized a benefit show, "Huddle Up for Tommy O: A Benefit for a Good Friend," set for Sept. 17 at Sweetwater Music Hall in Mill Valley. He'll be joined onstage by Grateful Dead bandmate Phil Lesh as well as Stu Allen & Mars Hotel.

"We've been through a lot of changes together," Weir said. "As friends, we talk things over. I said, 'OK, what if you die? We have to look at that.' My contention is that death is the last and best reward for a life well lived. And we agree on that. If Tommy dies, I figure he's in great shape, so I'm not worried about that."

That's an attitude that Olivier seems to accept with relief, knowing that he doesn't have to worry about others, that he can concentrate instead on getting well.

"Bobby tells me he isn't going to go around kicking any furniture if I die," Olivier said, sounding amused. "We know he's going to carry on no matter what, and I'm going to do the same. It's an ebb and flow deal, but I'm fighting the good fight. A positive attitude is the main thing that's keeping me on the right path. From my standpoint, I have a growing appreciation for how precious life is. I feel very, very fortunate to have all the moments I have now."

He and Weir agree that the main reason their friendship has endured is their ability to stay in the present, to forget the past and let the future take care of itself.

"We're two individuals who live very much in the moment," Olivier said. "We don't dwell on the past or the future. That gave us an instant bond. It's allowed us to just be ourselves."

Weir, who'll be 65 in October, has never been one to look in the rearview mirror, and, as he gets older, he doesn't even try.

"I don't have the wherewithal to dwell on the past," he said drily. "My memory isn't what it used to be."

In 1988, Weir won the Mill Valley Flag Football League's Golden Cleat Award, "given each year to the player who best embodies the concept of fair play and camaraderie." Olivier won it in 2004.

As the Chiefs begin a new season, their two award-winning stars will no longer be in the starting lineup. They may be sidelined, but they are both still very much in the game, the one all of us play every day.

"In March, when we learned that Tommy was under the weather, so to speak, it wasn't that big a change," Weir told me. "We just said, 'Where do we go from here? Let's look at it one day at a time.' Like today we're going to watch a ball game together. And we still get our workouts in. It's what we do. Given what our days bring, we try to keep each other on task and enjoy each other's presence. We just carry on like we always have."